This invention relates to carburetors, and in particular, to carburetors of the type described in U.S. Pat. No. 4,298,549.
There is a continuing demand for improved internal combustion engines in terms of performance, fuel efficiency and pollution, and one of the significant components in achieving these sometimes conflicting improved performances is the carburation. Some carburetor designs which are satisfactory during normal operation encounter problems with cold starting of the engine. One conventional approach to improved cold starting is to enrich the air-fuel mixture during starting, and this has been accomplished by various means in past designs. One object of the present invention is to provide a new and improved cold starting carburetor and in particular, a carburetor design which has improved cold starting while being simple and reliable. A further object is to provide a carburetor utilizing a pre-mix air supply to the fuel nozzle, with the amount of air supplied being varied during normal operation of the engine, and with this pre-mix air supply being shut off for cold starting. An additional object is to provide such a carburetor in which the duration of the cold start function is determined by a timing operation rather than by engine operation.
In present carburetor designs, such as that shown in the aforesaid U.S. Pat. No. 4,298,549, a valve member moves to control flow of fuel to the fuel nozzle of the carburetor. In order to maintain the engine running during idling, a bypass passage is provided through the valve member so that there is always a small and predetermined flow of fuel for idling. However, the amount of fuel flow required for idle varies with different engine sizes and when a carburetor utilizes a bypass passage in the fuel valve member, different members with different size passages have to be provided for different engine sizes. Accordingly, it is another object of the present invention to provide a fuel valve with adjustable idle bypass passage, permitting use of a single carburetor with various engine sizes.
These and other objects, advantages, features and results will more fully appear in the course of the following description.